Frost On Roof Sheathing

When the moisture gets into the attic it condenses on the roof sheathing in the form of frost.

Frost on roof sheathing.

Several online posts mostly from american sources say that any frost is not normal and signals impending doom. I have no bathroom vents or anything bad like that sourcing moisture into the attic. Before getting concerned you need to make sure the lack of frost is due to the roof itself and not from outside forces. And here s the clincher.

Warm shingles don t allow frost to form as readily as cold shingles. After spending a lot of time on gba i believe the best approach is to put exterior foam on the roof sheathing as we are looking to replace the shingles this summer due to the damage that was caused to the shingles to remove the ice dams and the fact that the builder never applied any ice water guard. Frost and ice forms in attics when warm humid air accumulates and condenses on the underside of your roof sheathing. Melting frost can lead to deteriorated roof sheathing mold on the roof sheathing wet insulation and water stains on the ceilings.

Depending on the temperature and the insolation ie. When moisture gets into the attic it condenses on the roof sheathing in the form of frost. One theory is that the walls have been demo s for a 2 3 week period on the interior and the heat from the interior is mixing with the cold air from the exterior creating frost on the inside of the sheathing. Left unchecked frost in an attic can lead to serious mold and decay.

The nails there are icy too but the rest of the roof sheathing and trusses look fine. That heat then conducts up all the way to the shingles. However if nothing is different about your home compared to your neighbors you may have a problem. That warm air makes contact with the roof deck and warms it up.

If the morning sun directly hits your home and not your neighbors lack of frost may just be attributed to the sun s heat. Frost itself doesn t do any damage but once it melts things get wet and then damage occurs. Can sun get to the roof you will have either frost or water collecting. Frost on underside of roof sheathing it s more likely a vapor problem than a liquid water problem.

The problems you pointed out are certainly real and need repair but getting the underside of the decking frosted requires vapor. The frost itself doesn t do any damage but once it melts things get wet which is when the damage. That s about it pretty simple. My question is is a little bit of frost normal in canada.

In the parlance of building scientists these cold wooden house parts make up a condensing surface much like a cold glass of ice tea beads with water on a hot summer day.